/**
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.lucene.search.function;

import org.apache.lucene.index.IndexReader;
import org.apache.lucene.search.FieldCache;

import java.io.IOException;

/**
 * Expert: obtains the ordinal of the field value from the default Lucene 
 * {@link org.apache.lucene.search.FieldCache Fieldcache} using getStringIndex().
 * <p>
 * The native lucene index order is used to assign an ordinal value for each field value.
 * <p
 * Field values (terms) are lexicographically ordered by unicode value, and numbered starting at 1.
 * <p>
 * Example:
 * <br>If there were only three field values: "apple","banana","pear"
 * <br>then ord("apple")=1, ord("banana")=2, ord("pear")=3
 * <p>
 * WARNING: 
 * ord() depends on the position in an index and can thus change 
 * when other documents are inserted or deleted,
 * or if a MultiSearcher is used. 
 *
 * @lucene.experimental
 *
 * <p><b>NOTE</b>: with the switch in 2.9 to segment-based
 * searching, if {@link #getValues} is invoked with a
 * composite (multi-segment) reader, this can easily cause
 * double RAM usage for the values in the FieldCache.  It's
 * best to switch your application to pass only atomic
 * (single segment) readers to this API.</p>
 */

public class OrdFieldSource extends ValueSource {
    protected String field;

    /** 
     * Constructor for a certain field.
     * @param field field whose values order is used.  
     */
    public OrdFieldSource(String field) {
        this.field = field;
    }

    /*(non-Javadoc) @see org.apache.lucene.search.function.ValueSource#description() */
    @Override
    public String description() {
        return "ord(" + field + ')';
    }

    /*(non-Javadoc) @see org.apache.lucene.search.function.ValueSource#getValues(org.apache.lucene.index.IndexReader) */
    @Override
    public DocValues getValues(IndexReader reader) throws IOException {
        final int[] arr = FieldCache.DEFAULT.getStringIndex(reader, field).order;
        return new DocValues() {
            /*(non-Javadoc) @see org.apache.lucene.search.function.DocValues#floatVal(int) */
            @Override
            public float floatVal(int doc) {
                return arr[doc];
            }

            /*(non-Javadoc) @see org.apache.lucene.search.function.DocValues#strVal(int) */
            @Override
            public String strVal(int doc) {
                // the string value of the ordinal, not the string itself
                return Integer.toString(arr[doc]);
            }

            /*(non-Javadoc) @see org.apache.lucene.search.function.DocValues#toString(int) */
            @Override
            public String toString(int doc) {
                return description() + '=' + intVal(doc);
            }

            /*(non-Javadoc) @see org.apache.lucene.search.function.DocValues#getInnerArray() */
            @Override
            Object getInnerArray() {
                return arr;
            }
        };
    }

    /*(non-Javadoc) @see java.lang.Object#equals(java.lang.Object) */
    @Override
    public boolean equals(Object o) {
        if (o == this)
            return true;
        if (o == null)
            return false;
        if (o.getClass() != OrdFieldSource.class)
            return false;
        OrdFieldSource other = (OrdFieldSource) o;
        return this.field.equals(other.field);
    }

    private static final int hcode = OrdFieldSource.class.hashCode();

    /*(non-Javadoc) @see java.lang.Object#hashCode() */
    @Override
    public int hashCode() {
        return hcode + field.hashCode();
    }
}
